1. Field of the Invention
The present invention relates to systems and methods of winding metal tubing into coils.
2. Description of the Prior Art
There are many different devices that contain coils made from hollow tubing. Such coils are commonplace in refrigerators, air conditioners, dehumidifiers and the like. When manufacturing such coils, a straight piece of metal tubing is connected at one end to a mandrel. The mandrel is then rotated, thereby cause the metal tubing to wind around the mandrel and create the desired coil. Such prior art coil production techniques work well for metal tubing that has thick walls. With such a thick walled tubing, the strength of the tubing itself prevents the tubing from crushing or buckling as it is wound around the mandrel. However, metal tube coils are made of many different materials and with many different wall thicknesses. In many applications, the strength of the tubing itself is insufficient to withstand a traditional winding procedure.
One application of a metal tube coil is described in co-pending patent application Ser. No. 09/702,636, entitled Hydrogen Diffusion Cell Assembly And Its Method Of Manufacture. In such an application, a coil is produced from palladium or a palladium alloy. Furthermore, the tubing is extremely thin walled, having an average wall thickness of between 0.001 inches and 0.005 inches. Such a thin walled tubing cannot be wound into a coil using prior art coil winding techniques. If such a thin walled tube were to be connected to a mandrel and wound in a traditional manner, the forces applied during the winding procedure would crush the tubing flat and/or cause the tubing to buckle.
A need therefore exists for a method and system that can be used to wind very thin walled tubing into coils. The need is met by the present invention as it is described and claimed below.
The present invention is a system and method of winding a length of tubing into a coil. The system uses a mandrel to wind a length of tubing into the form of a coil. However, prior to winding, the length of tubing is both internally pressurized and placed under tension prior to being wound around the mandrel. The tension experienced by the length of tubing causes the tubing to conform to the shape of the mandrel as the mandrel rotates. The internal pressurization of the tubing keeps the diameter of the tubing round as it is wound around the mandrel. As such, the tubing is prevented from crushing or bulking as it is wound around the mandrel.
The tension force applied to the length of tubing can be either constant or variable, depending upon the winding technique used. A constant tension force is used when the elongation of the length of tubing is left to chance. A variable tension force is used when the elongation of the length of tubing is monitored and controlled.